Despite good design and high-quality manufacture, there is an ever-present danger that the blades of power-driven rotary lawn mowers will become disconnected from their drive shafts, and will thereupon be ejected from the shroud or housing of the machine. This can occur for example due to impact of the blade upon rocks and other obstructions, or as a result of failure of the normal mounting structure due to other causes.
Although certain dangerous features of rotary power lawn mowers have previously been recognized, the patent art appears to be concerned primarily with the provision of means for protecting against objects that may be thrown by the blade. Illustrative United States patents include the following:
Machovina U.S. Pat. No. 3,481,124 discloses a grid-type guard that is disposed across the bottom of a lawn mower housing to protect the user from flying objects, and to prevent contact with the rotating blade.
Raniero U.S. Pat. No. 4,205,510 discloses a lawn mower apparatus comprising a cutting wheel disposed within a blade cover, and a protective housing supported thereon.
Frantello U.S. Pat. No. 4,189,905 substitutes monofilament cutters, disposed on a compressible spool hub, for conventional metal blades.
Rodish U.S. Pat. No. 4,357,789 utilizes a blade assembly in which the cutting elements are torsion spring members which project from a ring-like structure attached to a hub by a set of spokes.
Consequently, it is an object of the present invention to provide a novel fail-safe system for preventing ejection of a conventional rotary lawn mower blade, upon accidental disconnection or failure of its normal mounting structure.
A more specific object of the invention is to provide such a system which is of symmetrical form, so as to introduce no imbalancing effect into the machine on which it is installed.
Additional objects are to provide such a system which is relatively inexpensive to produce and facile to install, which can be provided as an add-on assembly, and which can be used with minimal modification to standard blades.
A further object of the invention is to provide a novel power-driven rotary lawn mower into which a fail-safe system having the foregoing features and advantages is incorporated.